1. Field of the Invention
The present invention relates to instrument displays generally and, more particularly, but not by way of limitation, to a novel instrument display employing a soft stop for homing.
2. Background Art
While the present invention is described for illustrative purposes only as being applied to a stepper motor driven analog instrument in a vehicle instrument display, it will be understood that it is applicable as well to any instrument display in which it is desirable to avoid using a hard stop for homing.
Instrument displays have been developed which use stepper motors to drive pointers, the pointers indicating, for example, vehicle speed or engine speed. Due to an inherent characteristic of a stepper motor, the stepper motor is in an indeterminate state following power-up. To "orient" the instrument after power-up, the motor is driven against a hard stop, so that the controller knows the position of the stepper motor and, therefore, the position of the pointer from then on until power is removed. This is accomplished by driving the pointer toward the hard stop, or the home position, a distance sufficient to accommodate the worst case pointer position. Typically, the hard stop coincides with the "zero" position of the pointer and may be a pin against which the pointer is driven. After this initial setting of the pointer at the home position, the controller then inferentially knows the position of the pointer.
While the above arrangement is satisfactory for the examples noted, there is interest in adding a instruments which read out values that cover greater than 360 degrees, or greater than a full circle. This presents a problem in that, since the pointer is required to rotate greater than 360 degrees in either direction, there can be no hard stop provided for homing purposes. A possible solution is to employ an optical sensor; however, this would add significant cost to the instrument. A similar problem exists where an instrument does not read out values that cover greater than 360 degrees, but where in instrument requires that the pointer swing either side of a home position.
Accordingly, it is a principal object of the present invention to provide a homing system for stepper motor driven display instrument which homing system does not require the use of a hard stop.
It is a further object of the invention to provide such a homing system that is economical and easily implemented.
Other objects of the present invention, as well as particular features, elements, and advantages thereof, will be elucidated in, or be apparent from, the following description and the accompanying drawing figures.